Apparatus for making post-stressed reinforced cement-concrete structures



Jan. 15, 1963 A. E. BRICKMAN 3,072,994

APPARATUS FOR MAKING POST-STRESSED REINFORCED CEMENT-CONCRETE STRUCTURESOriginal Filed June 6, 1955 2 SheetsSheet 1 g] 1 Q INVENTQR. h ALANE.BR|CKMAN Jan. 15, 1963 A. E. BRICKMAN 3,072,994

APPARATUS FOR MAKING POST-STRESSED REINFORCED CEMENT-CONCRETE STRUCTURESOngmal Filed June 6, 1955 2 Sheets-Sheet 2 aim /IIII IIIIIIIIIIM l I'I'I'IA INVENTOR. ALAN E. BRICKMAN United States Patent Office 3,072,994Patented .i'an. 15, 1963 3,072,994 APPARATUS FOR MAKING POST-STRESSEDREIN- FGRCED QEMENT-CONCRETE STRUCTURES Alan E. Brickman, 281 Dale Road,Wethersfield, Conn. Original application June 6, 1955, Ser. No. 513,314,now Patent No. 2,950,517, dated Aug. 30, 1960. Divided and thisapplication Aug. 23, 1960, Ser. No. 51,372

7 Claims. (Cl. 25118) This invention is concerned with post-stressedreinforced cement-concrete structures of considerable length andconsiderable width such as, for example, concrete highways, airportrunways, and the like, and directed in particular to the stressed metalreinforcement members embedded in such concrete structures. Moreespecially, it has to do with the application of tension to the metalreinforcement members in such structures.

The present application is a division of my copending application,Serial No. 513,314, filed June 6, 1955, entitled Method of MakingPost-Stressed Reinforced Cement-Concrete Structures, and now to beissued as Patent No. 2,950,517, dated August 30, 1960.

The application of prestressed concrete, in which pretensioned steel orother reinforcement members are incorporated in a concrete element orstructure, has been quite commonly used heretofore in the constructionof various types of concrete structures such as bridge girders, beams,floor slabs, etc. In making such concrete structures the steelreinforcing or tension members, such as stranded wire structures, arestressed to a predetermined tension within the form, after whichconcrete is poured into the form or before the poured concrete hasstarted any appreciable set. After the concrete has set the form isremoved and the bond of the concrete to the metal reinforcement membersreacts on the concrete to place it under compression. The most commonway of applying tension to the stranded wire structures is by means of acone socket member secured to each end of the stranded wire structure bymeans of a wedge with the socket members having a threaded portion whichcan be drawn up in various ways to apply the tensile stress.

To obtain the necessary prestress in the concrete, the strandedreinforcement is stressed initially under a tension on the order of 60%on its elastic limit values and in this condition applies compressionforces to the adjacent concrete in a manner that puts the entireconcrete structure in compression. In this state, stresses due totemperature changes and thermo-contraction which normally would causecracking of the concrete are counteracted by the initial tension forcesreleased by said reinforcing members and transmitted to the concretethereby setting up compression therein and preventing occurrence ofcracking or warping thereof.

Prestressing, however, has not been used extensively in cement-concretehighway construction because of the absence of a satisfactory means forapplying tension to the steel or other metal reinforcement rods or wireswhich usually run lengthwise in the longitudinal direction of thepavement and are necessarily of a fixed length so that the pavementdesign therefore is not continuous but formed in slab units of aprescribed length which is considerable and would be so great as not toprovide any practicable method of accomplishing the bringing of theindividual metal reinforcement rods or wires under a condition oftensile stress during the laying of the wet pavement.

In accordance with the present invention, I have provided a practicalmeans of tensioning, herein termed as post-tensioning, whereby eachreinforcing tension member of a system of metal reinforcement consistingof steel or other metal rods or wires of uniform cross-section is placedunder tensile stress through an external pulling force applied to oneend or to both ends of each rod or wire, the tensioning being carriedout in conjunction with the laying of the wet pavement. The rods orwires in being placed under tension are secured to anchorage memberstemporarily afiixed on the road forms. Both the anchorage members andthe reinforcing tensioning rods preferably are centered with respect tothe thickness of the pavement or halfway of the height of the roadforms.

In accordance With my post-tensioning, the ultimate tensile stressplaced on the reinforcing members is not applied until after theconcrete has been poured and some initial set of said concrete has takenplace. In the practice of my invention, tension is applied to each ofthe individual metal reinforcement members in one or more stages tolengthen them to a predetermined extent and to place them underprescribed tensile stress. For example, in the first tensioning stage, atensile force is applied to the metal reinforcement rods or wires tosecurely fasten their ends within the limits of their anchorage to theroad forms. In the second tensioning stage, additional tension isapplied to each metal rod or Wire after the concrete has been poured.Due to the combined weight of the wet concrete to that of the road formsit is possible to apply greater tension at this stage thereby bringingthe reinforcing tension members into proper position in the center ofthe slab Where they properly belong. After the concrete has set for ashort time, such as, for example, approximately 1 /2 hours, full tensionthen is applied to the reinforcing tension members and they are sosecured and maintained for the life of the pavement.

Apparatus embodying the present invention includes anchorage membersadapted to be temporarily supported by the road forms inside the area inwhich the wet pavement is to be poured, and such apparatus additionallyincludes a number of detachable tension-applying means externallyoperated outside of the form and connectable through the forms to endcouplings provided with step portions for stretching the rods or Wiresto a predetermined extent and placing them under a precalculated orknown tensile stress.

Upon prestressment of the rods or Wires to the ultimate required tensilestress, the externally-operated tension-applying means are detached fromthe stepped couplings on one or both ends of the reinforcing rods orwires and the latter then remain so tensioned by being securely held bytheir anchorage members to the road forms. The anchorage members areinitially attached to the inside face of the road forms and aredemountable therefrom so that they stay permanently in the concreteafter the road forms are stripped from the finished pavement.

It therefore is an object of my invention to provide apparatus wherebypretensioned reinforced concrete struc tures of considerable length andconsiderable width for use as pavements in concrete highways, airportrunways, and the like, can be made, in which the individual metalreinforcement members are brought under a condition of predeterminedtensile stress by tension applied in two or more stages.

Another object of the invention is to provide a practical apparatuswhereby a prestressed reinforced concrete structure of considerablelength and width can be made in which the pavement will be continuous inboth longitudinal and transverse directions and devoid of longitudinaljoints and the numerous transverse expansion joints that characterizesuch concrete structures made in accordance with the present practice.

A further object of the invention is to provide apparatus of thischaracter which is efficient, comparatively simple and practical in itsconstruction and operation.

These and other objects will be more apparant after referring to thefollowing specification and accompanying drawings, in which:

FIG. 1 represents a top plan view of a length of concrete highway duringconstruction in accordance with my invention with a portion of thepavement being shown broken away to disclose the stressed diagonaltension members for reinforcing the concrete, and also showing themanner in which such metal reinforcement members are placed undertension and so maintained anchored to the various anchorage saddlestherefor temporarily carried by the road forms during this stage of thehighway construction;

FIG. 2 is a fragmentary plan view, on enlarged scale,

7 showing a side edge portion of the highway of FIG. 1

including two adajacent anchorage members each having a pair of diagonaloppositely-inclined tensioned reinforcement members secured thereto invarious stages of tensioning, and the means associated with bothanchorage saddles for tensioning the reinforcement members thereof;

FIG. 3 is a side elevation of the fragmental pavement portion of FIG. 2,as viewed from the outside of a road form with the tensioning means forone of the anchorage members removed to show the slotted opening in theform side through which said tensioning means is inserted into theanchorage saddle for alternate connection to the ends of the twodiagonal reinforcement members thereof for tensioning the same;

FIG. 4 is a fragmentary cross-sectional view of the concrete pavementshown in FIG. 1 and taken along the line 4 -4 of that figure, looking inthe direction of the arrows;

FIG. 5 is an enlarged fragmentary plan view, partly in section, of oneof the numerous anchorage saddle members for initially securing thetensioned reinforcement members to the road forms and which,subsequently, is detached therefrom and embedded in the concrete, andincluding a pair of tensioned reinforcement members in place, one beingshown secured in the position assumed in the first stage of tensioningthereof and the other being shown secured in its final tensionedposition; and also showing one of, the tension-applying means associatedwith the anchorage saddles in alternate positions thereto for tensioningsaid reinforcement members respectively into their above-mentionedstressed positions;

FIG. 6 is an enlarged end elevation of the anchorage saddle withattached road form of FIG. 5 taken substantially on line 66 and showingthe road form partly in section;

FIG. 7 is an end view of one of the stepped-wing tensioning couplingmembers as viewed from the threaded open socket end thereof;

FIG. 8 is a side elevational view of the coupling member shown in FIG. 7and as viewed from the right side thereof;

FIG. 9 shows an end portion of one of the metal reinforcement members tobe stressed and having secured thereon a swaged fitting which is to bereceived within the socket portions of the coupling members of FIG. 7;and

FIG. 10 is a view of a reinforcement or tension member having swagedfittings on both its ends.

Referring in detail to the drawings, and more specifically to FIGURE 1thereof, the stressed reinforced elonone embodiment of my invention isshown in the form of a concrete highway and is generally indicated bythe reference nuinerallt). As indicated at the left-hand end portion ofFIGURE 1 where the concrete section is broken away, there are, exposed anumber of stressed metal rein- .explained more in detail later. 'Thesereinforcement members are placed approximately 12 to inches apart withinthe trough defined bythe longitudinal road forms gated body or structureof cement-concrete constituting d 13 and are arranged in oppositelyinclined groups diagonally with respect to the pavements length forsubstantially the full width of the pavement, and they are in contactwith each other where they cross, as indicated at 14.

It is to be understood that there may be provided conventionalsupporting chairs (not shown) at the intersections of crossingreinforcements to eliminate the catenary sag thereof prior to thepouring of the concrete. Such a system of diagonally-inclined metalreinforcements permits theme of rods or wires of relatively short lengthwhose ends are readily accessible to accomplish the bringing of the rodsor wires under various conditions of tensile stress during laying of thewet pavement and without interruption of the continuity of the latter.

The road forms 13 are temporarymold parts which are fixedly arranged atopposite sides of the pavement during construction thereof, and they areprovided at uniform intervals along their inside faces with a series ofdemountable anchorage saddle members 15 to each of which are anchoredtwo oppositely inclined diagonallyextending reinforcement members 12which are brought into an ultimate condition of predetermined tensilestress in a manner and by means as will be hereinafter described.

As shown in FIGS. 2, 3 and 4, the road forms 13 are held in place to thesub-grade during construction of the highway by means of form stakespassing through apertures in a series of brackets 16, as presently willbe described, these brackets being disposed at uniform intervalslongitudinally along the outer faces of each of the road forms. Accuratespacing between the road forms is accomplished by means of plates 17arranged for longitudinal sliding movement on the bottom of the formbetween suitable transversely spaced abutments l8 and 19, the

plates 17 each being formed with an angular slot 20 through which isdriven the usual form stake 21 which passes through a central transverseslot 22 of the web 23 of the bracket 16 and like underlying transverseslot 23 in the base of forms 13 (see FIG. 3) thus fixedly anchoring theform to the subgrade. By driving the plates 17 lengthwise of the forms,in either direction, the opposed road forms 13 may be moved in or outwhereby the spacing between them may be accurately adjusted to aprescribed dimension.

As illustrated in FIGS. 3 and 5, the vertical sides of the road forms 13at each location of an anchorage saddle member 15 is provided withsuitable apertures 24 for the fastening bolts 24' which support theanchorage saddle members 15 in initial assembly on the inside face ofthe side forms 13, and a slotted opening 25 for insertion therethroughof a tension-applying device 26 temporarily associated with eachanchorage saddle, as will be hereinafter described in detail. The sameslotted opening 25 serves for passing the tension-applying device 26 foralternate connection with a pair of socketed tensioning coupling members28 connected with the ends of the reinforcing rods 12 associatedwith'each of the anchorage saddles 15 and having step by-stepinterlocking engagement therewith as the rods are placed in tension, aswill be hereinafter described. The slotted openings 25 and the anchoragesaddle members 15 on opposite sides of the road forms are in alignmenttransversely of the pavement, as represented in FIG. 1.

The single rods or .wires of uniform cross-section employed as thereinforcement or tension members 12 in accordance with the practice ofmy invention are preferably of cylindrical form as shown in FIGS. 6, 9and 10, and made of a steel with elastic limits in the range of from190,000-220,000 pounds per square inch.

The words rods or wires of uniform cross-section as herein used, areintended to specify a standard rod or wire which is commercially smoothand whose circular crosssection is approximately uniform to such adegree as shall be readily and commercially feasible in the process ofmanufacture. A rod or wire of hard drawn steel of approximately /8 inchin diameter and a tensile strength of 195,000 pounds per square inch isfound to be advantageously suited for this purpose in practice. Also ainch diameter steel wire having a tensile strength on the order ofbetween 200,000216,000 pounds per square inch also would be practicable.

It is found that when a inch steel rod of the type having theabove-mentioned tensile strength value is stressed under a tension onthe order of 60% of its elastic limit value, the elongation for a 48foot length will be on the order of 2.4 inches which would be theultimate elongation or extent to which each reinforcing tensioning rodhas been stretched at the completion of the final tensioning stage whenthe tensioning force is applied to one end only of the reinforcing rod.If the reinforcing tension rods or wires 12 are placed under therequired tensile stress through an external pulling force applied toboth ends of each rod or wire, then for a rod of the abovestateddiameter and elongation characteristics the extent of stretch orelongation obtained when stressed under a tension on the order of 60% ofits elastic limit value would be 1% inches and, therefore, the socketedtensioning coupling members 28 then would be only half the lengthrequired when tensioning is efiected at only one end of each of the rodor wire reinforcements.

In FIGS. 9 and 10 I have shown a reinforcing tension member 12 whichconsists of a rod made of high tensile steel having afiixed apredetermined distance apart thereto a pair of abutments or swagedferrules 30 with the ends 31 of the rod extending through and projectinga short distance beyond the ferrules. Distance L between the opposedinner ends of the ferrules 30 must be accurately determined for theparticular type and size of steel rod employed so that a prescribedinitial tension will be applied to each tension member prior to pouringof the wet concrete within the side forms 13. Prior to swaging theferrules 30 on the ends of each of the reinforcing rods 12 the rod isinserted through the socketed coupling members 28. The portion of therod 12 on which the ferrules 30 are swaged have been prepared withsurface indentations into which ferrule metal cold flows under swagingand so develops the required stripping strength.

The anchorage saddle members are of identical construction so that thedescription of one will suffice for the others, and as shown in FIGS. 5and 6, each comprises an open-sided hollow casting having oppositelyinclined oblique end walls 33 and 34 connected by an inwardly curvedfront wall 35. The end walls 33 and 34 as well as the top and bottomwalls 36 and 37 respectively terminate in a vertical plane at the openback of the casting whereby the latter may be mounted in flat seatingengagement with the inside face of the road forms 13 when attachedthereto by the fastening bolts 24 which have threaded connection withsuitable web portions 38 cast in the anchorage saddles. Suitable top andbottom stabilizing flanges 39 and 40 may be provided bordering the openside of the casting, if desired.

As shown in FIGS. 5 and 6, the end walls 33 and 34 of the anchoragesaddle casting have a butterfly-shaped opening 41 and an elongatedslotted opening 42 therethrough. Mounted within the butterfly-shapedopenings 41 of each anchorage saddle for both longitudinal adjustmenttherein and slight axial rotation thereof are two of the socketedtensioning coupling members 28 provided for connecting thetension-applying device 26 to the ends of the pair ofdiagonally-extending reinforcing rods 12 during tensioning thereof andfor securing them in their various tensioned states to their particularanchorage saddle mem bers 15.

As best shown in FIGS. 7 and 8, the tensioning coupling members 28 arealike in their structure in which each has an elongated body portion 44formed with an enlarged 6 rod 12 and having a central hole 46 at theother end for insertion therethrough of the main rod portion of thereinforcing member 12. The entrance end of the bore 45 is internallythreaded as indicated at 47 for connection with the tension-applyingdevice 26 as will be hereinafter described.

The body portion 44 is of partially cylindrical formation as shown inFIG. 7, and it is provided exteriorly on opposite sides thereof withwing extensions 48 and 49 each having a series of lip steps 50, 51 and52 for locking, in turn, behind the back edge of portions of the endwalls 33 and 34 bordering the circular portions of the butterflyshapedopenings 41 thereof through which pass the cylindrical body portions 44of the coupling members 28. The positions of the lip steps 50, 51 and 52are determined by the elongation characteristics of the particular rodor wire structure employed for the reinforcing tension members 12. Thelip steps 50, 51 and 52 respectively are situated at identical positionsbut on'reversed faces of the wing extensions 48 and 49 so that at thecompletion of each tensioning stage the corresponding lip steps of bothwing extensions will be interlocked at the same time with the end walls33 and 34 of the anchorage saddle members 15.

For stretching and initially tensioning the reinforcing tension members12 so as to draw up the coupling members 28 in the first stage oftensioning of the rods or wires, a hand lever device 55 may be used of atype such as depicted in FIGS. 1 and 5, said device having a fulcrum arm56 one end of which is provided with a lug 57 adapted to be fulcrumed onthe anchorage saddle casting 15 through the aperture 42 so that when thecoupling 28 is forced inwardly of the saddle casting 15 by the pad 57 onthe operating handle of the device 55 the first lip step 50 will engagebehind the inside edges of the butterfly slots of the openings 41 in theend walls 33 and 34 of the casting and be held thereby after theindividual coupling members 28 are given a little twist about theiraxes, as depicted in FIG. 6. The tension-applying devices 26 areattached to each socketed coupling member 28 to effect the slighttwisting movement thereof above-mentioned, and before pouring of theconcrete, to assure not losing the first stage hitch in the tensioningoperation as well as for drawing it up in the remaining two stages oftensioning.

As shown in FIG. 5, this tension-applying device 26 comprises a longdraw screw 53 having threaded connection at its lower end with theinternally threaded socket portion 47 of a coupling member 28, this drawscrew passing through the slotted opening 25 in the road form 13 and asuitable aperture in a transverse web member 59 of the saddle casting15. A nut 60 having threaded connection with the outer end of the drawscrew 58 bears against the outer end of a metal sleeve member 61 whichis loosely mounted on the draw screw and has its inner end seatedagainst the confronting face of the web mem ber 59. Manual turning ofeach of the nuts 60 by suitable ratchet wrenches in an appropriatedirection operates to draw up the socketed coupling members 28 into theanchorage saddle members 15 to a point where the lip steps 50 of thewings 48 and 49 can shoulder seat by being engaged behind the butterflyslots 41 and locked thereby upon slight axial twisting movement of thecouplings by means of a wrench applied to the squared head 58' of thedraw screw 58.

In the second stage of tensioning, tension is applied to thereinforcement members 12 after the concrete has been poured between theroad forms 13 but before appreciable setting of the concrete hasstarted, the socketed coupling members 28 at this time being furtherdrawn into the anchorage saddle members 15 until the intermediate lipsteps 51 of the wings 48 and 49 can shoulder seat by being engagedbehind the butterfly slots 41 and locked thereby upon being turned intoa twisted position by wrench turning the squared head 58.

After the concrete has further set on the order of an 7 hour or more,additional tension is applied to the reinforcement members 12' by thedraw screw tensioning device 26 to. further draw up the soc etedcoupling members 28 in the anchorage members 15 to their third step 52following which they are twisted into locking engagement with the endwalls 33 and 34 of the anchorage saddle members 15. Obviously there willbe no restraint to the torsional reaction of the coupling members 23during twisting by the draw screw 53 by wrench turning its head 58 inthe first or initial stage of tensioning of the reinforcement members1'2. However, in the second stage of tensioning of the reinforcementmembers 12 it is found necessary to subject the couplings 28 totorsional force sufficient to twist the wings 43 and 49 in the wetconcrete to bring about second stage locking of the couplings by meansof the step lips 51.

To assure this second stage locking of the couplings 28 I effect therequisite additional torsional reaction on the draw screw 58 through useof the wrench on the squared end 53 thereof. This procedure also isemployed for securing additional torsional force to efiect third stagelocking of the couplings 23 to their respective anchorage saddle members15 by means of the step lips 52, in which instance the wings 48 and 49of the coupling 23 will have been drawn substantially completely insideof the saddle castings and, consequently, do not form a restraint totwisting which otherwise would be impossible in hardened concrete.

The reinforcing tensioning members 12 may be provided throughout theireffective length with a coating of grease, asphalt, or similar material,or may be jacketed with a vinyl or similar plastic, so as to break bondwith the concrete as may be necessary in the final tensioning step.After the concrete has hardened and set, the draw screw 58 of thetension-applying device 26 then is unscrewed from the socket portion ofthe coupling member 28 and the bolts 24 which hold the anchorage saddlemembers 15 in assembly with the road forms 13 are removed so that theroad forms can be stripped from the finished pavement for installationand use in the construction of subsequent pavement laying operations.The anchorage saddle members 15 with the socketed coupling members 28left inside remain embedded in the concrete after stripping of the roadforms 13.

A particular advantage in stressing reinforced concrete structures ofthe class described in accordance with my invention, is that thepavement slab can be made considerably thinner to withstand the sameloading as a pavement slab having the common fabric type of reinforcement. The design and proper arrangement of the pretensioned diagonalreinforcing tension members permit compression of the concrete therebyin two directions at the same time, viz., laterally and longitudinally,with the com plete elimination of all tensile stress in the concretebody. Furthermore, all joints can be eliminated so that continuity ofthe pavement may be obtained. Thus, a dual lane highway may be poured,two lanes at a time, omitting the center longitudinal joint'as well asthe usual transverse joints commonly used in a non-prestressedconstruction.

The term concrete as used herein comprehends mixtures of Portlandcement, or other hydraulic cement, with water and any other suitablematerial such as sand and/ or crushed stone.

It is to be understood that stranded wire structures can be substitutedfor the rod or wire reinforcing members and jacketed in the mannerabove-explained for the purpose of breaking bond with the concrete.

=l.rApparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like comprising a road form, an anchorage member on saidroad form and to which the ends of a pair of metal reinforcing tensionmembers under tension are to be securely fastened, said anchorage memberhaving two butterflyshaped openings therein facing in oppositelyextending oblique directions, coupling members having wing extensionsadapted to be received in the butterfly-shaped openings in saidanchorage member and be capable of slight turning movement therein, eachof said wing extensions being of stepped formation for successiveinterlocking engagement with said anchorage member during step-bysteptensioning of the reinforcing tension member, said coupling members eachbeing formed with an open-ended socket portion adapted to receive aferrule attached to a reinforcing tension member and formed with a holeat the other end to pass the intermediate body portion of thereinforcing tension member, the entrance opening of the socket portionof said coupling member being inter-- nally threaded, a draw screwhaving threaded connection at its lower end with the internally threadedsocket portion of one of said coupling members, a sleeve member aroundsaid draw screw and arranged for its lower end to bear against a part ofsaid anchorage member, a nut adapted to be threaded on the upper end ofsaid sleeve to apply a predetermined tension to said tension member byappropriate turning of the nut on said draw screw to pull the couplingmembers up into interlocking positions with the anchorage member.

2. Apparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like comprising a road form, an anchorage member on saidroad form and to which an end of a reinforcing tension memher undertension is to be securely fastened, said anchorage member having anopening therein adapted to receive an element with wing extensions onits opposite sides, a coupling member having oppositely extendingexternal wing extensions adapted to be received in the opening in saidanchorage member, said wing extensions each being of a stepped formationadapted for successive interlocking engagement with said adjacentanchorage member during periodic step-by-step tensioning of thereinforcing tension member so as to apply a predetermined tension tosaid tension member in reaching each of its successive stages oftensioning, said coupling member being formed with an open-ended socketportion adapted to receive a ferrule attached to the end portion of thereinforcing tension member and formed with a hole at the other end topass the intermediate body portion of such reinforcing tension member,the entrance opening of the socket portion of aid coupling member beinginternally threaded, a draw screw having threaded connection at itslower end with the internally threaded socket portion of said couplingmember, a s eeve member around said draw screw and arranged for itslower end to bear against a part of said anchorage member, a nut adaptedto be threaded on the upper end of said draw screw and to bear againstthe upper end of said sleeve to apply a predetermined tension to saidreinforcing tension member upon appropriate turning of the nut on saiddraw crew to pull the coupling member step-by-step into positions forinterlocking with the anchorage member, and means associated with saiddraw screw adapted for turning the latter manually to effect slighttwisting of the coupling relative to said opening and to swing and locksaid wing extensions step-bystep to said anchorage member as therespective steps of the wing extensions are successively pulled by saidnot and the draw screw into positions where such interlocking can beeffected during tensioning of the reinforcing tension member associatedwith said coupling member.

3. Apparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like comprising a road form having a slotted openingthrough its upright wall, a hollow open-sided anchorage member attachedto said road form over said opening and to which the ends of a pair ofmetal reinforcing tension members under tension are to be securelyfastened, said anchorage member having two butterfly-shaped openingstherein facing in oppositely extending oblique directions, couplingmembers having wing extensions adapted to be received in thebutterfly-shaped openings in said anchorage member and be capable ofslight turning movement therein, each of said wing extensions having aseries of step lips for successive interlocking engagement with saidanchorage member during step-by-step tension ing of a reinforcingtension member associated with each coupling member, said couplingmembers each being formed with an open-ended socket portion adapted toreceive a ferrule attached to a reinforcing tension member and formedwith a hole at the other end to pass the intermediate body portion ofsuch reinforcing tension member, the entrance opening of the socketportion of said coupling member being internally threaded, a draw screwpassing through said slotted opening in said road forms for'alternateconnection to said coupling members, said-draw screw having threadedconnection at its lower end with the internally threaded socket portionvof one of said coupling members, a sleeve member around said draw screwand arranged for its lower end to bear against a part of said anchoragemember, a nut adapted to be threaded on the upper end of said draw screwand to bear against the upper end of said sleeve to apply apredetermined tension to said reinforcing tension member uponappropriate turning of the nut on said draw screw to pull the couplingmembers step-bystep into positions for interlocking with the anchoragemember, and means associated with said draw screw adapted for turningthe latter manually to effect slight twisting of the coupling in theparticular butterfly-shaped opening and to swing and lock the step lipsof said wing extensions to said anchorage member as the respective steplips are successively pulled by said nut and the draw screw intopositions where such interlocking can be effected during tensioning ofthe particular reinforcement member.

4. Apparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like, comprising, in combination, a fixed road side form,a hollow anchorage member carried by said road form and to which theends of two oppositely inclined converging metal reinforcing tensionmembers when under tension are to be securely fastened, said anchoragemember having openings therein through which are inserted and housedsuch converging ends of said tensioning members, adjustable couplingmeans individual to said tension members as well as being mutuallyassociated with said anchorage member and movable relative thereto, saidindividual coupling means having a stepped formation made up of definitelip steps adapted for successive interlocking detention relative to thesame anchorage member of ferrules fast on such converging ends of saidreinforcing tension members and contained therein during periodicstep-by-step tensioning of the latter so as to apply a predeterminedtension to said tension members in reaching each of their successivestages of progressive tensioning, and adjustable prestressing meansincluding a draw screw element operatively connected with either of thesaid individual coupling means and effective to adjust the latterstep-by-step separately on the common anchorage member intopredetermined stages of tension-applying lip step positions thereonwhereby each lip step will act in turn to apply a predetermined fixedamount of tension to the particular metal reinforcing tension memberassociated with the said coupling means as will be required preparatoryto depositing a pourable wet concrete mixture in this apparatus, andthereafter when the stages of partial solidifiit) cation, hardening, andsetting of such wet concrete mix occur there-in.

5. Apparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like comprising a fixable side road form, a hollowanchorage member demountable on said road form and to which an end of atransverse reinforcing tension member under tension is to be securelyfastened, said anchorage member having an apertured opening thereinadapted to re ceive and movably cooperate with an element with wingextensions on its opposite sides, an elongated adjustable couplingmember having oppositely extending external side wing extensions adaptedto be movably received in the opening in said anchorage member and to beadjusted longitudinally thereinto, said coupling member having aninternally threaded socket portion adapted to receive thereinto aferrule attached to a reinforcing tension member and also arranged atthe other end to pass outwardly therethrough the longitudinalintermediate portion of such reinforcing tension member, said Wingextensions on the coupling member each being of a stepped formationhaving several lip steps adapted for successive interlocking engagementwith said adjacent anchorage member during periodic step-by-steptensioning of the reinforcing tension member so as to apply apredetermined tensionto said tension member in reaching each of itssuccessive stages of tensioning, the positions of said lip steps beingdetermined by the elongation characteristics of the metal employed forthe reinforcing tension member whereby the latter will be stretched andbrought to a condition of predetermined tensile stress at each of saidlip step locations, the last of which being effective to permanentlymaintain the solidified and hardened concrete in a continual state ofcompression, and tension-applying draw means on the said anchoragemember including a draw screw element disposed through said openingthereof and having threaded connection with the internally threadedsocket portion of said coupling member whereby step-by-step adjustingmovements of the latter can be effected relative to said anchoragememher into several predetermined stages of tension-applying lip steppositions thereon.

6. Apparatus for making prestressed elongated reinforced concretestructures of considerable length and considerable width for use as ahighway or the like comprising a fixable side road form, a hollowanchorage member demountable on said road form and to which the ends ofa pair of diagonally-extending metal reinforcing tension members undertension are to be securely fastened, said anchorage member having twobutterfly-shaped openings therein facing in oppositely extending obliquedirections, elongated coupling members having wing extensions adapted tobe movably received in the butterfly-shaped openings in said commonanchorage member and to be capable of slight turning movement oninsertion within the latter for subsequent adjustment of theirrespectively positions, each of said coupling members having aninternally-threaded openended socket portion adapted to receivethereinto a ferrule attached to a reinforcing tension member and formedwith a hole opening at the other end to pass outwardly therethrough thelongitudinal intermediate portion of the reinforcing tension member,said wing extensions each being provided with several lip steps adaptedfor successive interlocking engagement with the associated anchoragemeans during periodic step-by-step tensioning of the reinforcing tensionmembers, the positions of said lip steps being determined by theelongation characteristics of the metal employed for the reinforcingtension members whereby the latter will be stretched and brought to acondition of predetermined tensile stress and each of said lip steplocations, the last of which being effective to permanently maintain thesolidified and hardened concrete in a continual state of compression,and draw means interchangeably mounted on said anchorage memberincluding ademountable draw screw disposed through either of saidbutterfly-shaped openings and having threaded connection with theinternally-threaded socket portion of the particular coupling memberoccupying said opening whereby separate step-by-step adjusting movementsof such coupling member can be effected relative to said anchoragemember and in predetermined stages of tension-applying lip steppositions thereon.

7. In combination, a fixed road form, a hollow anchorage memberdemountably carried by said road form and adapted for receiving thereinan anchoring thereto one end portion of an exterior elongatedconcrete-reinforcing metal tension member which is required to beembedded in a solidified concrete slab moulded in situ with said roadform, an exterior elongated concrete-reinforcing metal tension memberfixed at one end and carrying an abutment fast on and adjacent its otherend in which said abutment-carrying end last-named is disposed towardand directed into said anchorage member and is capable of longitudinalmovement thereinto upon subsequent elongation and consequent tensioningof said metal tension member, stepped means mutually associated withsaid abutmentand said anchorage member and movable relative to thelatter, said stepped means having a portion thereof provided with screwthreads, and movable draw means on said anchorage member including adraw screw disposed therethrough threadingly connected with said steppedmeans effective to adjust the latter outwardly of said anchoring memberand effect longitudinal tensioning and elongation of said tension memberthrough the agency of said stepped means and said engaged abutment, saidstepped means having its ofiset parts adapted to serially engage saidanchoring member and retain said reinforcing tension member in itsseveral successive stepby-step predetermined positions and also to applyto the latter member definite amounts of stress as it is brought undertension by adjustment of said movable draw means.

References Cited in the file of this patent UNITED STATES PATENTS903,909 Steiner Nov. 17, 1908 2,655,846 Freyssinet Oct. 20, 19532,833,186 Dobell May 6, 1958 FOREIGN PATENTS 1,006,760 France Jan. 30,'1952 147,743 Australia Aug. 8, 1952 OTHER REFERENCES Road Prestressed,Engineering News, Redord, April 12, 195 1.

1. APPARATUS FOR MAKING PRESTRESSED ELONGATED REINFORCED CONCRETESTRUCTURES OF CONSIDERABLE LENGTH AND CONSIDERABLE WIDTH FOR USE AS AHIGHWAY OR THE LIKE COMPRISING A ROAD FORM, AN ANCHORAGE MEMBER ON SAIDROAD FORM AND TO WHICH THE ENDS OF A PAIR OF METAL REINFORCING TENSIONMEMBERS UNDER TENSION ARE TO BE SECURELY FASTENED, SAID ANCHORAGE MEMBERHAVING TWO BUTTERFLYSHAPED OPENINGS THEREIN FACING IN OPPOSITELYEXTENDING OBLIQUE DIRECTIONS, COUPLING MEMBERS HAVING WING EXTENSIONSADAPTED TO BE RECEIVED IN THE BUTTERFLY-SHAPED OPENINGS IN SAIDANCHORAGE MEMBER AND BE CAPABLE OF SLIGHT TURNING MOVEMENT THEREIN, EACHOF SAID WING EXTENSIONS BEING OF STEPPED FORMATION FOR SUCCESSIVEINTERLOCKING ENGAGEMENT WITH SAID ANCHORAGE MEMBER DURING STEP-BYSTEPTENSIONING OF THE REINFORCING TENSION MEMBER, SAID COUPLING MEMBERS EACHBEING FORMED WITH AN OPEN-ENDED SOCKET PORTION ADAPTED TO RECEIVE AFERRULE ATTACHED TO A REINFORCING TENSION MEMBER AND FORMED WITH A HOLEAT THE OTHER END TO PASS THE INTERMEDIATE BODY PORTION OF THEREINFORCING TENSION MEMBER, THE ENTRANCE OPENING OF THE SOCKET PORTIONOF SAID COUPLING MEMBER BEING INTERNALLY THREADED, A DRAW SCREW HAVINGTHREADED CONNECTION AT ITS LOWER END WITH THE INTERNALLY THREADED SOCKETPORTTION OF ONE OF SAID COUPLING MEMBER, A SLEEVE MEMBER AROUND SAIDDRAW SCREW AND ARRANGED FOR ITS LOWER END TO BEAR AGAINST A PART OF SAIDANCHORAGE MEMBER, A NUT ADAPTED TO BE THREADED ON THE UPPER END OF SAIDSLEEVE TO APPLY A PREDETERMINED TENSION TO SAID TENSION MEMBER BYAPPROPRIATE TURNING OF THE NUT ON SAID DRAW SCREW TO PULL THE COUPLINGMEMBERS UP INTO INTERLOCKING POSITIONS WITH THE ANCHORAGE MEMBER.